Avoidance of "having" should not be seen as a hard and fast rule. The use of "having" can sometimes create a stylistically awkward, heavy-handed sentence, but this does not mean that you will never, under any circumstances, see a correct GMAT sentence with "having". In fact, you might sometimes find a legit GMAT sentence that happily keeps a 'having".

The key when it comes to judging stylistic flaws (as opposed to grammatical mistakes - which are outright incorrect) is that superior vs inferior style is a RELATIVE matter. You must compare the five answer choices - rule out anything that is an outright grammatical error or makes the sentence plainly illogical. After that, if you see a sentence with "having" and another one which is perfectly acceptable and also has the added advantage of not having "having" - you can go ahead and chuck out the sentence with "having".

@Ilana@MasterGMAT - > to suport your assertion with a GMATPrep question.

Some patients who do not respond to therapies for depression may simply have received inadequate treatment, having, for example, been prescribed a drug at a dosage too low to be effective or having been taken off a drug too soon.

(A) having, for example, been prescribed a drug at a dosage too low to be effective or having been
(B) having, for example, a drug prescription that was ineffective because the dosage was too low, or being
(C) as, for example, having too low of a dosage of a prescribed drug for it to be effective, or being
(D) when they have, for example, been prescribed too low a drug dosage to be effective, or were
(E) for example, when they have a drug prescription with a dosage too low to be effective, or been

Oa is A

In this Sentence Correction question we should proceed by first eliminating grammatically unacceptable or illogical constructions:

Answer choice B is illogical as it shifts the meaning from the action of being prescribed a low dosage ("having been prescribed" as an example of inadequate treatment) to possession of a prescription "having a drug prescription"). Note that "having" in answer B is not a helping verb, as it is in answer choice A - the similarity of the first and second "having" is simply a mirage.

C is also awkward for the same reason - "having" goes from being a helping verb "having been prescribed" becomes simple possession "having a low dosage". This is not the original intention of the sentence. In addition, the pronoun "it" is ambiguous in this answer choice/

D should be eliminated because the use of the conjunction "when" is inappropriate. The sentence describes a generalization, and "when" implies particular occurrences. The modifiers are illogically placed "too low a drug dosage to be effective" is less clear than "a drug dosage to low to be effective". "too low" and "to be effective" should be placed together.

E similarly corrupts the logic by replacing the helping verb "having" with "have" - mere possession of a prescription rather than the action of being given an inappropriate prescription by doctors.

This leaves A as the default - the only logically constructed and stylistically clear sentence, despite the so-called 'ugliness' of 'having'. The rule to remember is that a correct GMAT sentence, might be ugly, but if it is grammatically correct, logical and clearer than the alternatives, we can embrace its ugliness.

that's an excellent response. You have brutally killed poor choices .

more questions to follow

Excellent explanation....
I was able to reach A by looking for parallelism across or ( and of course the topic name which made it easier:))